In recent years, there are cases where a shaft of a centrifugal compressor is rotatably supported by magnetic bearings in order to achieve a high-speed revolution. With the shaft being supported by the magnetic bearings in this manner, no frictional heat is generated between the shaft and the bearings. Therefore, it is possible to prevent the shaft and the bearings from having galling due to frictional heat, and to rotate the shaft at high speed.
This type of magnetic bearing is not brought into direct contact with the shaft, and hence does not have a strength high enough to support the weight of the shaft. Therefore, for example if the shaft is unintentionally displaced from the reference position due to a power failure or an earthquake, to thereby be brought into contact with the magnetic bearing, the magnetic bearing may be damaged.
Therefore, the centrifugal compressor whose shaft is supported by the magnetic bearings is provided with auxiliary bearings which, when the shaft is displaced from the reference position, are brought into contact with the shaft to suppress a further displacement of the shaft. With these auxiliary bearings being provided, even if the shaft is displaced from the reference position from any cause, contact between the shaft and the magnetic bearing is prevented, and hence, the magnetic bearing is not damaged.